A subject matter of an invention is a device for individual quench hardening of technical equipment components, i.e. for controlled hardening of individual components using a cooling medium, aiming to minimize deformation.
Quenching is a heat treatment process applied to steel, consisting in the rapid cooling of workpieces from the austenitizing temperature down to near-ambient temperature. Quench hardening results in the transformation of steel microstructure and improvement of both mechanical and usable properties, e.g. durability, hardness, wear resistance, etc.
Various existing solutions involve quenching conducted in dedicated devices or quenching chambers, in different liquid cooling media, such as: oil, water, salt or—less frequently—in gases or air. For the time being, oil remains the most common quenching medium.
Quench-hardened workpieces are usually arranged in batches on dedicated equipment (trays, baskets, etc.), constituting so-called workloads, or they are placed in bulk on conveyor belts to be heated in furnaces up to the austenitizing temperature, and hardened in quenching devices. Quenching devices may be integral elements of austenitizing furnaces or separate, independent solutions.
A characteristic feature of all quenching devices is the presence of a unit designed for ensuring forced circulation of the cooling fluid—mixer in the case of liquids, and fans in the case of gases. Forced circulation of the cooling medium is necessary for effective transferring of heat from quenched workpieces to the heat exchanger, which—in turn—directs heat outside of the quenching device (usually using water or another external cooling medium). Consequently, the presence of one or more heat exchangers is also characteristic in classic quenching devices.
In conventional quench hardening devices the process proceeds as follows: after being heated to the austenitizing temperature, the workload is transported from the furnace to the quenching device in which cooling fluid absorbs heat, thus cooling the workload. Next, the cooling fluid (heated by the workload) is directed to the heat exchanger where it is cooled and redirected towards the workload to absorb heat. Optimum flow of the cooling fluid is ensured by mixers (for liquids) and fans (for gases), being directed by appropriate stators and ducts.
In addition to obtaining proper mechanical properties, in the quench hardening process it is important to minimize deformation caused by stresses resulting from temperature gradients and by transformation of material structure during quenching. Deformations require costly machining to smooth out the shape of individual elements, and therefore the goal is to minimize deformation and achieve maximum repeatability.
Theoretically, minimization of deformation can be achieved by providing identical and uniform cooling conditions both for a single workpiece and for all workpieces (which is particularly important in mass production). Conventional oil quenching results in increased deformation due to the three-phase nature of the process (steam cushion, bubble and convection phases) and the related non-uniform intensity of heat absorption. Similarly, it is not an optimum solution to arrange individual elements in batch workloads, because each workpiece—due to its unique position in the workload—undergoes the hardening process in a unique, different manner, eventually exhibiting deformation differing from other workpieces.
Given the above disadvantages of conventional quenching devices—in terms of minimization and repeatability of deformation—works have been initiated to develop a device for repeatable hardening of individual workpieces in a cooling medium.